The increasing use of lithium-ion batteries (LiBs) in electric vehicles and electronics has made efficient recycling essential for maintaining a reliable and affordable supply of critical metals. Thermal treatment of black mass (BM), the heterogeneous residue from spent LiBs, is a crucial step to improve downstream material separation and recovery. This study investigates the thermal behavior of LiBs BM by analyzing the thermal behavior of its components when heated to 600 °C in an inert (N2) atmosphere or in a mixture of 90 vol % N2 and 10 vol % H2. Thermogravimetric analysis (TGA) was conducted at a heating rate of 10 °C/min with an isothermal hold of 1 h, and coupled with quadrupole mass spectrometry (QMS). The analysis was performed on graphite, activated carbon, lithium hexafluorophosphate (LiPF6), polyvinylidene fluoride (PVDF), synthetic black mass, and lithium nickel manganese cobalt oxide (NMC) industrial BM. Equilibrium calculations conducted in FactSage 8.3 were used to describe and understand the experimental findings. The TGA results indicate that in 100 vol % N2, graphite exhibited the lowest weight loss of 0.1 wt %, followed by activated carbon at 2.9 wt %, PVDF at 56 wt %, and LiPF6 at 81 wt %. Synthetic black mass had a weight loss of 3.4 wt %, while industrial black mass had 1.0 wt %. In 90 vol % N2/10 vol % H2, LiPF6 and PVDF experienced weight losses of 79 and 64 wt %, respectively. Synthetic BM had a weight loss of 15.1 wt %, and industrial BM 15.6 wt % due to enhanced reduction of metal oxides in the presence of hydrogen.